Gradeability-based shift pattern control for an automatic transmission

In a motor vehicle including an engine, a transmission providing a plurality of successively increasing forward speed ratios through which the engine may drive the vehicle, a base shift pattern control for initiating upshifting and downshifting between said speed ratios in response to a comparison of measured load condition parameters with predetermined load condition parameters, and a range selector positionable by a vehicle driver to exclude at least one specified speed ratio from said base shift pattern, a method of operation comprising the steps of:

• determining an apparent grade load indication in relation to an imbalance between engine produced torque and an estimate of the torque required to achieve a current driving condition of the vehicle;
• determining maximum gradeability indications corresponding to a maximum grade load which can be overcome with said forward speed ratios;
• comparing said apparent grade load with said maximum gradeability indications to form an indication of excess gradeability of each such speed ratio;
• and
• overriding said base shift pattern when an excess gradeability indication for a respective speed ratio is less than a reference value by inhibiting upshifting to such respective speed ratio.

Control apparatus for a motor vehicle including an engine and a transmission providing a plurality of forward speed ratios through which the engine may drive the vehicle, the control apparatus comprising:

• means for initiating upshifting and downshifting between said speed ratios in response to a comparison of measured load condition parameters with predetermined load condition parameters defined by a base shift pattern;
• means for determining an apparent grade load indication in relation to an imbalance between engine produced torque and an estimate of the torque required to achieve a current driving condition of the vehicle;
• means for determining maximum gradeability indications corresponding to a maximum grade load which can be overcome with said forward speed ratios;
• means for comparing said apparent grade load with said maximum gradeability indications to form an indication of excess gradeability of each such speed ratio;
• and
• means for overriding said base shift pattern when an excess gradeability indication for a respective speed ratio is less than a reference value by inhibiting upshifting to such respective speed ratio.